Dark matter contraction and stellar-mass-to-light ratio gradients in massive early-type galaxies

Lindsay Oldham; Matthew Auger

doi:10.1093/mnras/sty065

paper

Dark matter contraction and stellar-mass-to-light ratio gradients in massive early-type galaxies

arXiv:1801.01887 · doi:10.1093/mnras/sty065

Abstract

We present models for the dark and luminous mass structure of 12 strong lensing early-type galaxies (ETGs). We combine pixel-based modelling of multiband HST/ACS imaging with Jeans modelling of kinematics obtained from Keck/ESI spectra to disentangle the dark and luminous contributions to the mass. Assuming a gNFW profile for the dark matter halo and a spatially constant stellar-mass-to-light ratio $Υ_{⋆}$ for the baryonic mass, we infer distributions for $Υ_{⋆}$ consistent with IMFs that are heavier than the Milky Way's (with a global mean mismatch parameter relative to a Chabrier IMF $μ_{α c} = 1.80 \pm 0.14$ ) and halo inner density slopes which span a large range but are generally cuspier than the dark-matter-only prediction ( $μ_{γ^{'}} = 2.0 1_{- 0.22}^{+ 0.19}$ ). We investigate possible reasons for overestimating the halo slope, including the neglect of spatially varying stellar-mas-to-light ratios and/or stellar orbital anisotropy, and find that a quarter of the systems prefer radially declining stellar-mass-to-light ratio gradients, but that the overall effect on our inference on the halo slope is small. We suggest a coherent explanation of these results in the context of inside-out galaxy growth, and that the relative importance of different baryonic processes in shaping the dark halo may depend on halo environment.

arXiv comment20 pages; accepted for publication in MNRAS

Dark matter contraction and stellar-mass-to-light ratio gradients in massive early-type galaxies

Abstract

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